1. Chapter 5(1) Color MaPPING

2. Outline Visualizing scalar data
A number of the most popular scalar visualization techniques
Color mapping
Contouring
Height plots
5.1 Color mapping
5.2 Design of effective colormaps
5.3 Contouring in 2D and 3D
5.4 Height plots

3. 5.1 Color Mapping Most widespread visualization method for scalar data
Associate color with scalar values
Methods for defining scalar-to-color function
Color look-up tables (colormap)
Transfer functions (more detail in Chp 9 &10)

4. 5.1 Color Mapping

5. 5.2 Designing effective colormaps
Attract user to certain value ranges or individual values
Colormap uses particularly salient colors
Colormap can be influenced by:
Application
Domain-specific convention &Traditions

6. 5.2 Designing effective colormaps
Fig 5.1. Construction of rainbow colormap (for weather applications: temp.; heat; height fields etc.)

7. 5.2 Designing effective colormaps
Listing 5.1. Rainbow colormap construction

8. 5.2 Designing effective colormaps
Some application, emphasize the variation of the data
Colormap containing two or more alternating colors
Many other colormap designs
Geographical application
Classical medical imaging

9. 5.2 Designing effective colormaps
Fig 5.2. Visualizing the scalar function with (a) a luminance colormap and (b) a zebra colormap. The luminance colormap shows absolute values, whereas the zebra colormap emphasizes rapid value variations.

10. 5.2 Designing effective colormaps
Fig 5.3. Medical visualization with luminance and rainbow colormaps

11. 5.2 Designing effective colormaps
Requirement for colormaps:
(1) invertibility; (2) linearity.
(3) scheme of color mapping:
Texture-based color mapping
Vertex-based color mapping
[The relationship among
the colormap design
scalar data variation speed
domain sampling frequency.]

12. 5.2 Designing effective colormaps
Fig 5.4. Texture-based color mapping. The sphere geometry is sampled with (a) 64 x 64 points, (b) 32 x 32 points, and (c) 16 x 16 points.
Advantage: produce reasonable results even for a sparsely sampled dataset

13. 5.2 Designing effective colormaps
Fig 5.5. Vertex-based color mapping. The sphere geometry is sampled with (a) 64 x 64 points, (b) 32 x 32 points, and (c) 16 x 16 points.
Advantage: simplicity and direct support by even low-end graphics hardware

14. 5.2 Designing effective colormaps
The choice of the number of Color N
A small N: color banding effect, artifact
Typical scalar visualization applications use 64 to 256 different colors
Other factors for Colormap
Geometric factors
User group
The medium used to present the visualization

15. 5.2 Designing effective colormaps
Fig 5.6. Color banding caused by a small number of colors in a look-up table.

16. 5.2 Designing effective colormaps
Conclusion:
Color mapping : generate color values from scalar values by
Colormap
Color transfer function
Design issues for effective colormaps:
Knowledge of the application domain conventions
Typical data distribution
Visualization goals
General perception theory
Intended output devices
User preference